Production of olefinic c4f8



Patented Nov. 11, 1952 "UNITED :sTA'T PRODUCTION or OLEFINIC can Bald Eagle, White Bear County, and Lyle J. Hals, gnors to Minnesota Mining ompany, St. Paul, Minn., a

.Wilbur H. Pearlson,

Township, Ramsey St. Paul, Minn., assi & Manufacturing C corporation of Delaware No Drawing. Application April 18, 1951, I

Serial No. 221,738

2 Claims.

This application is based upon, a mere amplification of, our prior Serial No. 163,332, filed May 20, 1950.

,The present invention relates to compounds containing carbon and fluorine. More particularly it relates to an improved method oi. making a particular fluorocarbon compound, namely olefinic C4F8.

Heretoiore certain unsaturated fluorocarbons have been prepared by first producin chlorofiuoro-carbon compounds and then by the use of a suitable reagent removing chlorine atoms from adjacent carbon atoms; thus yielding an unsaturated compound. Still others have produced certain olefinic fiuorocarbons by removal of l-ICl from chloro-fluoro-carbon hydrides.

"Although it does not concern our process or involve any teaching of the production of olefinic CrFa, Benning et a1. Patent No. 2,394,581 is referred to as a matter of general interest in this general field of chemistry.

' We have found that we can produce olefinic C4Fs, and more particularly pe-rfluoroisobutene, (CFs) 2C=-CF2, smoothly and in yields appreciably above 50% of pyrolysis of the cyclic C4F8UOmpOl-1n'd, octafiuoroand constitutes application cy-clobutane. The method of carrying out our process will now be illustrated by a specific example.

Example As apparatus we employed a carbon tube of /2 internal diameter, enclosed in iron pipe and heated over a 14 section by an electric furnace. The cyclic C4F8 (B. P. about -4= C.) was introduced into the carbon tube as a gas and passed through the heated section thereof. The products leaving the heated zone were condensed in traps cooled by liquid air. Temperatures were determined by a thermocouple placed between the iron casing and the furnace wall. Maintaining the temperature, at the point of the thermocouple, at TOO-725 0., we introduced aseous cyclic C4F8 into the carbon tube at such rate that 7.4 grams of the cyclic 04F8 were introduced and passed through the carbon tube during the period of about 15 minutes. Examination of the reaction product, condensed in the traps, showed that about 90% of the material had been pyrolyzed. The products were further analyzed by means of the infrared spectrum. Approximately 70% of the product was olefinic C4Fa, having a boiling point of about +5 to +6 C. at 740 mm. Another 20% of the product was shown to be unsaturated C3F6. The identity of these olefins is specifically established by the I the theoretical by the controlled characteristic infrared data for the 0:0 stretching frequency at 1798 canin the case of the C3Fc olefin and at 1750 cm? in the case of the C4Fs olefin. It should be noted that perfiuorobutene-l has its bond at 1795 cmr as do the other terminal straight chain olefins.

The C4Fa olefinic product was further identified by molecular weight determination. The molecular weight found was 200; whereas the molecular weight by calculation is also 200.

Oxidation of the C4F8 olefin product by aqueous neutral KMnO yielded perfiuoro-acetone,

proving beyond doubt that the C4Fs olefin is the isomer, perfluoroisobutene, (CF3)2C=CF'2. 26.4 g. of i-CtFc, B. P. +6.4" 0., g. KMnO4 and g. of water were heated in a metal bomb to about C. for a total of 4 hours and then cooled to room temperature. The low boiling gases were bled off and collected in a liquid air cooled trap. The ketone, (CF3) 2C0, i. e., the perfluoroacetone, was recovered from the aqueous reaction mixture by filtering off the solid manganese dioxide, destroying the excess permanganate with sodium bisulfite, and then extracting the ketone as the hydrate with ether. The ketone hydrate was concentrated in the resultant extract by distillation of the ether. The ketone was then liberated by treatment of the resulting concentrated hydrate with phosphorous pentoxide.

The ketone was found to boil at -26 C./74 =7 mm. and to have a mol. wt. of 163-168. The calculated molecular weight for CsFsO is 166. The reported boiling point for the ketone (CF3)2CO, is 26 C. The infrared spectrum of the ketone matches that of an authentic sample of the compound.

The conversion was 32%, the yield 31%.

Some departures from the temperature range of 700-'725 C. can be made and are contemplated.

However, in spite of variations in chargin rate, we have found that 600 C. is too low to provide any significant reaction. On the other hand, if temperatures are increased so that they approach 900 0., this leads to a very marked increase in the production of olefinic CaFs. In general the reaction temperature should be maintained within a restricted range and should not depart too widely from about NO-725 C. In other words.

the reaction temperature should be of the order of 700 C.

What we claim is:

1. A process which comprises passing a gaseous charging stock primarily consisting of octafluo- 4 rocyclobutane through a, heated tube maintained UNITED STATES PATENTS at a, temperature of the order of 700 C, and for a Number Name Date time sufficient to cause upwards of 50% conver- 2,384449 Benmng et all Sept 11, 1945 S1011 b0 olefinic C4F8, and recovering the latter. 2 3 4 21 Downing t 1 Sept. 1. 1 4 c g compwnd Perfiuomisobutene. 5 2,394,581 Benm'ng et a1 Feb. 12, 1946 3 2 4 2,404,374 Harmon July 23,-"1946 EARLSON' 2,406,153 Lewis Aug. 20, 1946 OTHER REFERENCES REFERENCES CITED 10 Miller et 211., Ind. and Eng. 39, 303, 401, (1947). The following references are of record in the Henne et al., J. A. C. S. 70, 130 (1948). file of this patent: 

1. A PROCESS WHICH COMPRISES PASSING A GASEOUS CHARGING STOCK PRIMARILY CONSISTING OF OCTAFLUOROCYCLOBUTANE THROUGH A HEATED TUBE MAINTAINED AT A TEMPERATURE OF THE ORDER OF 700* C. AND FOR A TIME SUFFICIENT TO CAUSE UPWARDS OF 50% CONVERSION TO OLEFINIC C4F8, AND RECOVERING THE LATTER.
 2. THE NOVEL COMPOUND, PERFLUOROISOBUTENE, (CF)2C=CF2. 